1. Filed of the Invention
This invention relates to a method of producing a conjugated diene polymer by using a novel catalyst of a rare earth element compound, and more particularly to a method of producing a conjugated diene polymer having excellent wear resistance and mechanical properties and a reduced cold flow by polymerizing a conjugated diene compound with a novel catalyst of a rare earth element compound and reacting the resulting polymer just after the polymerization with at least one compound selected from the group consisting of a halogenated organometal compound, a halogenated metal compound, an organometal compound, a heterocumulene compound, a hetero three-membered compound, a halogenated isocyano compound, a carboxylic acid, an acid halide, an ester compound, a carbonic ester compound and an acid anhydride as a modifying agent.
2. Description of Related Art
Since the conjugated diene polymers play an industrially very important role, there have hitherto been proposed many proposals for a polymerization catalyst of a conjugated diene compound in the production of the conjugated diene polymer. Particularly, many polymerization catalysts giving a high content of cis-1,4-bond have been studied and developed for providing conjugated diene polymers having high performances in the thermal and mechanical properties. For example, there are well-known catalyst systems containing a compound of a transition metal such as nickel, cobalt, titanium or the like as an essential component. Among them, some catalysts have industrially and widely been used as a polymerization catalyst of butadiene, isoprene or the like (see End. Ing. Chem., 48, 784(1956) and JP-B-37-8198).
On the other hand, a catalyst system comprising a rare earth metal compound and an organometal compound of an element of Group I-III has been studied and developed in order to attain a further higher content of cis-1,4-bond and an excellent polymerization activity, and also studies on a high stereospecific polymerization using the same have been actively conducted.
In JP-B-47-14729 is disclosed a catalyst system comprising a rare earth metal compound such as cerium octanoate or the like, an alkylaluminum hydride such as isobutylalumium hydride or the like, trialkyl aluminum and an aluminum halide such as ethylaluminum dichloride or the like. Particularly, there is a description that a catalyst activity is increased by maturating the catalyst system in the presence of butadiene.
In JP-B-62-1404, JP-B-63-64444 and JP-B-1-16244 is proposed a method that the catalyst activity is enhanced by increasing a solubility of a rare earth element compound in a polymerization solvent. And also, JP-B-4-2601 discloses that a catalyst system comprising a rare earth metal compound, trialkylaluminum or aluminum hydride, and an organic halogen derivative indicates a higher activity in the polymerization of 1,3-butadiene as compared with the conventional catalyst.
However, polymers obtained by using the conventional catalyst systems including the rare earth metal compound becomes wider in the molecular weight distribution and do not sufficiently improve the wear resistance and rebound resilience.
In JP-A-6-211916, JP-A-6-306113 and JP-A-8-73515 is reported that when a two-component catalyst system consisting of a neodymium compound and methylaluminoxane is used, a high polymerization activity is indicated and a conjugated diene polymer having a narrow molecular weight distribution is obtained. However, in this polymerization method, it is required to use a greater amount of methylaluminoxane as compared with the conventional catalyst system using the organoaluminum compound in order to hold the sufficient polymerization activity and obtain a polymer having a narrow molecular weight distribution, and hence it is required to remove a greater amount of a metal retaining in the polymer. Furthermore, such a two-component catalyst system is expensive as compared with the usual organo-aluminum compound and also the cold flow becomes large to cause a problem in the storage stability, so that it comes into problem in the practical use.
In order to solve these problems, JP-A-10-35633, and JP-A-10-306113report that the cold flow can be controlled by modifying the conjugated diene polymer polymerized in the presence of the catalyst system using the methylaluminoxane with a hetero three-membered compound, a halogenated metal compound, a metal carbonate or the like. In the latter case, however, the catalyst level is to high for obtaining a polymer having a narrow molecular weight distribution, and the amount of aluminoxane used can not be reduced to a practical level. And also, a greater amount of the organoaluminum compound is used, so that there is a problem in the removal of residual metal from the polymer.